The Optical Properties and Stability of GE and Sn-Doped TeO x Films
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THE OPTICAL PROPERTIES AND STABILITY OF GE AND Sn-DOPED TEOx FILMS
W-Y LEE, C. R. DAVIS, G. LIM, 11. COUFAL AND F. SEQUEDA IBM Almaden Research Center, San Jose, CA 95120
ABSTRACT The optical properties and the thermal stability of Ge and Sn doped TeOx films prepared by coevaporating Tee 2 , Te, Ge and Sn are reported. These films are amorphous as-deposited and crystalline Te appears after annealing at, e.g., 100 to 250°C. As expected, the addition of Ge and Sn increases the absorption of the TeOx films at the wavelength of interest (e.g., 830 nm). However, the thermal stability of (TeOi.1)1_xGex (x=0 to -0.7) films is found to decrease with increasing x initially, starting to increase with increasing x only after x reaches a value between 0.3 and 0.4. These results differ from those reported previously for Ge and Sn-doped TeOx films and from those observed for Te-Ge alloy films. Interpretations of these results based on a solid state reaction between Tee 2 and Ge or Sn during deposition are presented and discussed.
INTRODUCTION Tellurium oxide based optical recording media have generated a great deal of interest because of their reported reversibility when doped with Ge and Sn [1-4]. According to the published data, these media consist of elemental Te particles dispersed in an amorphous Tee 2 matrix. The recording is done by taking advantage of the changes in the optical properties, arising from the changes in the microstructure of the medium through the amorphous to crystalline phase transformation upon laser irradiation. Although it was stated that the addition of Ge and Sn was used to increase the stability and the crystallization speed of the medium, respectively, the detailed explanation of the effects of Ge and Sn doping on the reversibility of these media is not available. We have investigated the general optical properties and the effects of large-area pulsed-laser and oven annealing on the optical properties and the microstructure of TeOx, and Ge and Sn-doped TeOx films [5,6]. In this paper, the general optical properties and the stability of Ge and Sn doped TeOx films are reported. In particular, the effect of solid state reaction between Ge (or Sn) and Tee 2 during their coevaporation on the optical properties and the thermal stability of the resultant films is presented and discussed.
EXPERIMENTAL PROCEDURES Thin films of pure TeOx and TeOx doped with various concentrationsof Ge and Sn were deposited onto glass or PMMA substrates by thermally coevaporating Te, Tee 2 , and Ge or Sn from separate Knudsen cells. The desired x value and Ge or Sn doping concentration for each film was obtained by selecting appropriate Tee 2 , Te, Ge or Sn deposition rates measured with standard quartz crystal monitors. Laser annealing of these films was done with a 1 cm 2 excimer laser beam (308 nm, 40 nsec pulse width) having an energy density of -30 m1/cm 2 , while oven annealing was done in a nitrogen ambient with a heating rate of ~20*C/min. The changes in the optical reflectivity and transmission were monitored in-
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